This invention relates to improvements in a bit apparatus in which a cutter member having cutting teeth is axially supported on a shaft for rotation about the shaft, and which includes a bearing mechanism interposed between the cutter member and the shaft.
A known bit apparatus, such as a tri-con bit apparatus, includes a cutter member, which has cutting teeth, axially supported on a shaft so as to be rotatable about the shaft, and a bearing mechanism interposed between the cutter member and the shaft.
The bearing mechanism basically comprises at least a radial bearing for receiving load in the radial direction and a thrust bearing for receiving load in the axial direction. Beryllium-copper alloy and a hard-metal alloy, which exhibit durability to drilling impact when the bit apparatus is used, are the materials used to manufacture the radial and thrust bearings.
There are instances where the oil seal in a tri-con bit apparatus is destroyed during drilling, allowing muddy water to penetrate the interior of the bearing mechanism. Hard particles contained in the muddy water find their way into the bearing mechanism, causing the beryllium-copper alloy and hard-metal alloy to sustain wear. The problem with the conventional tri-con bit apparatus is a short overall service life caused by such wear in the bearing mechanism.
Accordingly, an object of the present invention is to provide a bit apparatus in which bearing-mechanism wear can be minimized to prolong service life.
According to the present invention, the foregoing object is attained by providing a bit apparatus in which a cutter member having cutting teeth is axially supported on a shaft for rotation about the shaft, and a bearing mechanism is interposed between the cutter member and the shaft, wherein the bearing mechanism comprises: at least a radial bearing for bearing a radially directed load and a thrust bearing for bearing an axially directed load; the radial bearing including a shaft-side split bearing member and a cutter-side split bearing member, the shaft- and cutter-side split bearing members being rotatable relative to each other.
In a preferred embodiment, the shaft-side split bearing member is formed to have an engaged portion for engaging with an engaging portion, which has been formed on the shaft, in such a manner that the shaft-side split bearing member will co-rotate with the shaft.
In a preferred embodiment, the cutter-side split bearing member is formed to have an engaged portion for engaging with an engaging portion, which has been formed on the cutter member, in such a manner that the cutter-side split bearing member will co-rotate with the cutter member.
In a preferred embodiment, a clearance on the order of 30 to 300 xcexcm is provided between the shaft-side split bearing member and the cutter-side split bearing member.
In a preferred embodiment, the radial bearing is a hard alloy in which a main ingredient is a tungsten carbide substance containing a cobalt substance of 5 to 20 mass percent.
In a preferred embodiment, wherein a diamond film is formed on at least one of the shaft- and cutter-side split bearing members and on mutually opposing surfaces of both of the members.
According to another aspect of the present invention, the foregoing object is attained by providing a bit apparatus in which a cutter member having cutting teeth is axially supported on a shaft for rotation about the shaft, and a bearing mechanism is interposed between the cutter member and the shaft, wherein the bearing mechanism comprises: at least a radial bearing for bearing a radially directed load and a thrust bearing for bearing an axiall directed load; the thrust bearing including a shaft-side split bearing member and a cutter-side split bearing member, the shaft- and cutter-side split bearing members being rotatable relative to and in sliding contact with each other.
In a preferred embodiment, the shaft-side split bearing member is formed to have an engaged portion for engaging with an engaging portion, which has been formed on the shaft, in such a manner that the shaft-side split bearing member will co-rotate with the shaft.
In a preferred embodiment, the cutter-side split bearing member is formed to have an engaged portion for engaging with an engaging portion, which has been formed on the cutter member, in such a manner that the cutter-side split bearing member will co-rotate with the cutter member.
In a preferred embodiment, a sliding-contact clearance on the order of 30 to 300 xcexcm is provided between the shaft-side split bearing member and the cutter-side split bearing member.
In a preferred embodiment, the thrust bearing is a hard alloy in which a main ingredient is a tungsten carbide substance containing a cobalt substance of 5 to 20 mass percent.
In a preferred embodiment, a diamond film is formed on at least one of the shaft- and cutter-side split bearing members and on sliding-contact surfaces thereof.
In a preferred embodiment, the engaged portion is a groove or notch.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.